1. Field of the Invention
The present invention relates to a circuit arrangement for processing satellite signals comprising a first circuit part, which is made as a processor for computing position and/or speed signals from satellite signals, a second circuit part, which is made as a real-time clock to provide a time signal, at least two voltage sources, which are provided to supply at least one circuit part, and switching means, which are provided for switching the supply of at least one circuit part between the first voltage source and the second voltage source, to a system with a circuit arrangement of this type, and to a method for operating a system of this type.
2. Description of the Background Art
A circuit arrangement known from being commercially available is set up for processing high-frequency electromagnetic satellite signals, which are emitted by satellites in orbit. The circuit arrangement is used, for example, in a receiver for a global positioning system (GPS receiver). The task of the circuit arrangement is substantially to process the encoded signals from satellites in such a way that position and/or time and/or speed signals can be made available for further processing, for example, by a navigation system. Because satellite signals are typically very weak signals, amplification with a low-noise amplifier (LNA) and signal conditioning are provided before the supplying of the encoded signals in the circuit arrangement. The amplified satellite signal is used as the input signal for a radio frequency semiconductor component (RF chip), which is provided for the conditioning of the input signal. The conditioned satellite signal is then provided for further processing to the circuit arrangement.
GPS receivers are used for GPS devices, which are configured as mobile handheld units or as built-in devices, for example, for navigation systems in vehicles, airplanes, or ships. Particularly during use of the GPS receiver in a mobile handheld unit such as a portable navigation system, supplying of the GPS receiver with electrical power typically occurs from several, mutually supplementary voltage sources. These voltage sources have different storage capacities for electrical power.
A first voltage source is provided for a normal mode of the GPS receiver and provides a sufficient amount of power for a prolonged time. Thus, in a normal mode, position and/or time and/or speed signals can be determined from satellite signals. In a normal mode of the GPS receiver, components such as the low-noise amplifier, the RF chip, and an oscillator, which provides a clock frequency, are turned on.
A second voltage source, which has a considerably lower storage capacity for electrical power than the first voltage source, in contrast, is designed only for a basic operation (sleep mode/shut-down mode), in which only data maintenance in the circuit arrangement is to be assured. No provisions are made for operation of the other components of the GPS receiver with the second voltage source. To switch between the two voltage sources and between the aforementioned operating modes, the circuit arrangement is assigned switching means. The switching means assure that a normal mode of the GPS receiver can occur with a sufficient supply voltage of the first voltage source. If the supply voltage of the first voltage source is too low, a switching is carried out by the switching means in the basic operation, to ensure the maintenance of data and/or settings in the circuit arrangement. As soon as the first voltage source is again provided with a sufficient supply voltage, the switching means can activate the normal mode automatically or if there is a turn-on command, which can be triggered by a user of the GPS receiver.
The switching between the normal mode and the basic state must be made by the switching means at a time when a minimum voltage and thereby a still sufficient amount of power can be provided by the first voltage source, to be able to perform an orderly switching. Otherwise, undefined switching states can occur in the GPS receiver, which can cause undesirable output signals from the circuit arrangement. A switching voltage, which is above the minimum voltage, is therefore established for the switching means.